The invention relates to sight flow indicators used to visually indicate flow through a conduit.
Sight flow indicators are often connected to a conduit to provide a convenient way of ascertaining whether a fluid is flowing through the conduit, for example, to see if fluid is flowing through an automatic sprinkler system conduit during testing of a fire protection system.
Lewis U.S. Pat. No. 1,179,441 discloses a sight flow indicator that has an inlet and outlet for connection to a pipe and employs two windows located on opposite ends of a sighting region of a flow passage of the indicator to permit viewing of bubbles or particles passing through the passage during flow through it. When turbid water was in the passage of such an indicator in use, a flash light would sometimes be used to assist in viewing flow.
Other sight flow indicators are described in Woodruff U.S. Pat. No. 2,847,969, which shows a flow indicator device consisting of a bladed element (FIG. 1) or three multicolor balls (FIG. 3); Windsor U.S. Pat. No. 2,520,869, which shows a piston that is displaced to indicate a flow condition; and Akhtarekhavari U.S. Pat. No. 4,474,209, which shows an impeller that is rotated within a glass cylinder by fluid flow.